Mitogenicity of streptococcal extracellular products and antagonism with concanavalin A

Extracellular products have been purified from group A Streptococcus pyogenes culture supernatant fluids and their mitogenicities have been tested on rabbit and mouse lymphocytes. Two fractions were mitogenic: the kappa-fraction (pI = 4.8, mol. wt. = 30,000), a protein which was identified as the erythrogenic toxin, and the epsilon-fraction (pI = 10.3, mol. wt. = 17,000) a glycoprotein, both stimulated rabbit and CBA mouse spleen cells. The stimulation of rabbit thymocytes was weak unless macrophages or 2-mercaptoethanol were added. A third product, the gamma-fraction (a protein, pI = 4.2, mol. wt. = 72,000) was very weakly mitogenic and had the capacity to reduce the stimulation induced by a T-cell mitogen, such as Con A, but not by a B-cell mitogen such as Nocardia.